1. Field of the Invention
The application relates to a method and a related communication device used in a wireless communication system and related communication device, and more particularly, to a method of handling radio resource control (RRC) connection reconfiguration and a related communication device in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as to user equipments (UEs).
In the LTE system defined by 3GPP, the logical connection between the UE and the E-UTRAN is defined by radio resource control (RRC) connection states. The RRC states of the UE contain an RRC_IDLE state and an RRC_CONNECTED state. Mobility control in RRC_IDLE is UE-controlled (e.g. cell reselection) while in RRC_CONNECTED it is controlled by the E-UTRAN.
In RRC_CONNECTED, the E-UTRAN allocates radio resource to the UE to facilitate the transfer of (unicast) data via shared data channels. To support this operation, the UE monitors an associated control channel which is used to indicate the dynamic allocation of the shared transmission resources in time and frequency.
A RRC connection reconfiguration procedure is used to establish, modify or release radio bearers (e.g. DRBs (Data Radio Bearer)). In LTE, RRC connection reconfiguration also involves setting up a default EPS (Evolved Packet System) bearer between the UE and a core network (CN). This EPS bearer is set up on the basis of a non-guaranteed bit rate allowing the application-level signaling to take place as soon as a secure RRC connection is established.
In addition, the same RRC connection reconfiguration procedure is employed to perform handovers, NAS (Non-Access Stratum) message transfer and configuration of measurements. However, certain types of reconfiguration cannot be performed until the AS (Access Stratum) security has been activated. As a part of the RRC connection reconfiguration procedure, the E-UTRAN sends an RRC connection reconfiguration message with the appropriate information elements. Upon a successful handover, the UE responds with a message “RRC connection reconfiguration complete”.
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system, considering relaying for cost-effective throughput enhancement and coverage extension. The LTE-A system includes all of the features of the LTE system and several new ones, the most important of which are: carrier aggregation (CA), enhanced multi-antenna support and relaying. The LTE system provides extensive support for deployment in spectrum allocations of various characteristics, with transmission bandwidths ranging from 1.4 MHz up to 20 MHz. In the LTE-A system, the transmission bandwidth can be further extended with carrier aggregation wherein multiple component carriers are aggregated and jointly used for transmission to/from a signal UE. In general, up to five component carriers can be aggregated, allowing for transmission bandwidth up to 100 MHz.
When CA is configured, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment, one serving cell provides the security input (one ECGI, one PCI and one ARFCN) and the NAS mobility information (e.g. TAI) similarly as in Rel-8/9 under 3GPP. This cell is referred to as the Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC). The configured set of serving cells for a UE therefore always consists of one PCell and one or more SCells.
The RRC connection re-establishment procedure will not be triggered by physical layer problem occurred in Scell. The Scells failure is handling by network, not by UEs. According to prior art, the network can obtain the RRC connection reconfiguration procedure to add/configure/release Scells. If a UE is unable comply with all the Scell configuration, e.g. adding a Scell, the UE will consider reconfiguration failure and perform RRC Connection re-establishment procedure. Nevertheless, it is not reasonable that the Scell failure result in the disconnection of Pcell.
In addition, the UE sets the reestablishmentCause to the value “reconfigurationFailure” while the re-establishment is resulting from the UE is unable to comply with the all the configurations included in the RRCConnectionReconfiguration message. After received the cause from a UE, the network cannot distinguish if the configuration failure is for PCell or SCell. The network may always consider the failure is for PCell configuration and adjust the PCell configuration. Nevertheless, if the configuration failure is for SCell, the UE will suffer the failure again. For example, the system information of SCell is control by the Scell. If the configuration failure is resulting from the UE is unable to comply with the SCell's system information. The configuration failure will be met again and again unless the network finds this.